Boris Johnson deliberately misled parliament multiple times over partygate, the Commons privileges committee has ruled.
The long-awaited report by the cross-party group of MPs was published on Thursday morning and accused the former PM of “serious contempt”.
In an angry statement, Johnson said the report was “the final knife-thrust in a protracted political assassination”.
He quit as an MP last week after being told in advance of its conclusions, launching a furious attack on the committee for conducting a “witch hunt”.
If he had not preempted the report by resigning, it is likely his punishment would have triggered a by-election in his seat as it called for a lengthy 90-day suspension.
The committee also said Johnson should be denied the right to have a former MP’s pass to parliament.
“We have concluded above that in deliberately misleading the House Mr Johnson committed a serious contempt,” the MPs said.
“The contempt was all the more serious because it was committed by the prime minister, the most senior member of the government.
“There is no precedent for a prime minister having been found to have deliberately misled the House.
“He misled the House on an issue of the greatest importance to the House and to the public, and did so repeatedly.
“He declined our invitation to reconsider his assertions that what he said to the House was truthful.
“His defence to the allegation that he misled was an ex post facto justification and no more than an artifice. He misled the committee in the presentation of his evidence.”
Johnson denied having lied to parliament when he repeatedly said Covid rules were followed in Downing Street.
The former prime minister said he made the assertion having been reassured by his staff it was true.
But the committee rejected his defence and accused him of being “complicit in the campaign of abuse and attempted intimidation of the committee”.
Johnson said: “This is rubbish. It is a lie. In order to reach this deranged conclusion, the committee is obliged to say a series of things that are patently absurd, or contradicted by the facts.
“For the privileges committee to use its prerogatives in this anti-democratic way, to bring about what is intended to be the final knife-thrust in a protracted political assassination – that is beneath contempt.”
In a last-ditch attempt to disparage the Tory-majority panel on the eve of publication, Johnson called for its most senior Conservative member to resign.
He accused Bernard Jenkin of “monstrous hypocrisy” after the Guido Fawkes website reported the MP had gone to a drinks party in parliament while Covid restrictions were in place in 2020.
But Lib Dem deputy leader Daisy Cooper said this was a “typical distraction tactic” from the ex-PM “that doesn’t change the fact he broke the law and lied about it”.
The committee is chaired by veteran Labour MP Harriet Harman but it has a Conservative majority.